Method of making a stand-up plastic bag

ABSTRACT

An improved method of making a stand-up plastic bag in which the side seam seals are formed at the same time as the gusset wall seals. The method includes the steps of supplying the film, folding the film to form the gusset, simultaneously forming the heat seals for the gusset walls and the side seams at one temperature, forming the heat seals to join the gusset walls together at a higher temperature, and separating the film into completed bags. The improved method provides greater efficiency and increased production rates.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of application Ser. No.303,310, filed Jan. 30, 1989, now U.S. Pat. No. 4,954,124, which is adivision of application Ser. No. 171,063, filed Mar. 21, 1988, now U.S.Pat. No. 4,837,849. The present invention generally relates to plasticbags and, more particularly, to a method of making a plastic bag capableof standing up by itself before, during, and after being filled.

So-called stand-up, free-standing or self-standing plastic bags arewell-known in the prior art. Representative of the prior art are theplastic bags disclosed in U.S. Pat. Nos. to Knuetter (2,265,075), Doyenet al (3,380,646), Kugler (3,437,258), Michel (3,715,074) and Bustin(4,353,497). Also, well-known in the prior art are plastic bagsincorporating a zipper-type closure device along the top opening ormouth of the bags. Representative of the prior art are the plastic bagsdisclosed in a U.S. Pat. No. to Ausnit (4,601,694) and a published U.K.Patent Application to Kirkpatrick (2,047,199). Further, U.S. Pat. Nos.to Kan (3,980,225 and 4,055,109) disclose a self-standing plastic bagwhich also incorporates a zipper-type closure device along its mouth.

Market research has shown that consumers greatly desire a stand-up,reclosable plastic bag because of the convenience of filling and storinghighly liquid foods and of microwave heating of foods directly in thebag. Some known stand-up bags attempt to provide the stand-up capabilitymerely by use of a simple bottom gusset alone or supplemented with sealsadded in the gusset structure. A simple bottom gusset sealed at itssides does not provide a normal consumer plastic bag with a sufficientstand-up feature. Such a plastic bag, typically made from polyethylenefilm of, for example, less than 1.0 mil thickness, is too limp to standup from the gusseted bottom.

Other plastic films of greater thickness and higher modulus can befabricated into a bag that will stand up from a simple bottom gusset.One plastic bag currently available uses a very deep bottom gussetdesign to provide certain advantages in food storage and microwaveheating, but some difficulty has been experienced in filling andemptying this bag. The bag does not stand up easily when empty, and thezipper-type closure is difficult to maintain open when filling andemptying this bag. Other currently-available stand-up bags seal thebottom gusset into a stand-up base that is much more stable than thesimple bottom gusset. The self-standing bag of the above-cited U.S.patents to Kan is an example of a bag having such stand-up base.

Erickson et al, U.S. Pat. No. 4,837,849, discloses an improved bag whichmeets consumer requirements for a stand-up reclosable plastic bag. Ithas a stronger, sturdier, more stable stand-up base which supports thebag while it is empty and during and after filling. It also has morereliable leak-proof side seams. The method of making the bag disclosedtherein includes three separate sealing steps of a continuous web:sealing the interior surfaces of the gusset to form the base (bottomseal), sealing the side walls of the bag (side seam seal), and sealingthe exterior gusset walls (gusset edge seal).

Precise registration of the web in the machine direction is critical forproper bag appearance and stand-up stability. Registration refers to theproper machine direction spacing of the seal bars so that the bottomseal and each of the side seals are aligned correctly. Because of therapid line speeds involved as the continuous bag web is sealed at eachstation, consistent good registration of the bottom seal and the sideseam seal may be difficult to achieve.

Therefore, there remains a need in the art for a method of makingstand-up reclosable plastic bags which provides proper alignment of thebottom and side seam seals.

SUMMARY OF THE INVENTION

The present invention meets that need by providing a method of making astand-up plastic bag in which the bottom and side seam seals of the bagsare in correct alignment. The method of the present invention providesgreater efficiencies in the production of stand-up reclosable bags.

The stand-up plastic bag produced by the process of the presentinvention comprises a pair of front and rear side walls which define anopen mouth at upper edges of the side walls, and a pair of front andrear bottom gusset walls disposed between the side walls. The front andrear side walls and the front and rear bottom gusset walls are composedof a multi-layered film of first and second heat-sealable thermoplasticmaterials. The first material is on interior surfaces of the walls andheat-sealable at a temperature within a first temperature range. Thesecond material is on exterior surfaces of walls and heat-sealable at atemperature within a second temperature range greater than the firsttemperature range.

The bottom gusset walls have upper portions that are interconnectedtogether to define a bottom wall extending between the front and rearside walls. The bottom gusset walls also have lower end portions joinedby heat seals to lower end portions of the front and rear side walls atcontiguous portions of the first material on the interior surfacesthereof.

The heat seals which join the bottom gusset walls extend upward alongopposite longitudinal edges of the front and rear side walls and thefront and rear bottom gusset walls to join the walls at contiguousportions of the first material on interior surfaces thereof.

The bottom gusset walls further have opposite longitudinal edges joinedtogether by heat seals at contiguous portions of the second material onthe exterior surfaces thereof.

In accordance with one aspect of the present invention a method formaking a stand-up plastic bag comprises the steps of: supplying amulti-layered film of the first and second heat-sealable thermoplasticmaterials and folding the film to form the front and rear side walls andthe front and rear bottom gusset walls disposed between the side wallswith interior surfaces of the walls having the first material thereonand exterior surfaces of the walls having the second material thereon.The first heat sealable material is sealable within a first temperaturerange, while the second heat-sealable material is sealable within asecond temperature range which is higher than the temperatures in thefirst range.

Heat seals are formed simultaneously by heating the film to within thefirst temperature range and joining lower end portions of the front andrear bottom gusset walls with corresponding lower end portions of thefront and rear side walls at contiguous regions of the first material onthe interior surfaces thereof. This forms a bottom wall of connectedupper portions of the front and rear bottom gusset walls which extendbetween the front and rear side walls. The heat seals further join thefront and rear side walls with the front and rear bottom gusset wallsalong opposite longitudinal edges thereof at contiguous portions of thefirst material on the interior surface of the longitudinal edges of thewalls.

Heat seals are then formed along the gusset edge, by heating the film towithin the second temperature range and joining the front and rearbottom gusset walls together along their opposite longitudinal edges atcontiguous portions of the second material on the exterior surfacesthereof. The film is then separated into completed plastic bags bysevering the film through at each of the heat seals at each of thelongitudinal edges of the walls.

Accordingly, it is an object of the present invention to provide animproved method of making a plastic bag that has a stable stand-up basecapable of supporting the bag whether empty or full and having correctlyaligned bottom and side seam seals that is more efficient and allowsincreased production rates. Other objects and advantages of the presentinvention will be apparent from the following description, theaccompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a stand-up plasticbag constructed in accordance with the method of the present invention.

FIG. 2 is an enlarged cross-sectional view of the bag taken along line2--2 of FIG. 1.

FIG. 3 is another enlarged cross-sectional view of the bag taken alongline 3--3 of FIG. 1.

FIG. 4 is yet another enlarged cross-sectional view of the bag takenalong line 4--4 of FIG. 1.

FIG. 5 is still another enlarged cross-sectional view of the bag takenalong line 5--5 of FIG. 1.

FIG. 6 is a block diagram of the apparatus for carrying out the methodof the present invention for making a stand-up plastic bag, and also afront elevational view of the bag of the first embodiment as produced bythe method.

FIG. 6A is a front elevational view of a section of the film webrepresenting one bag blank moving through the apparatus of FIG. 6,illustrating the condition of the bag blank after the film folding,gusset forming, and closure locking operations have been completed bythe apparatus.

FIG. 6B is another front elevational view of the same bag blank movingthrough the apparatus of FIG. 6, illustrating the condition of the bagblank after the gusset/side sealing operation has been completed.

FIG. 6C is yet another front elevational view of the same bag blankmoving through the apparatus of FIG. 6, illustrating the condition ofthe bag blank after the gusset edge sealing operations have beencompleted.

FIG. 7 is a side plan view of a second embodiment of a stand-up plasticbag constructed in accordance with the method of the present invention.

FIG. 8 is a perspective view of the bag of the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference is made to FIGS. 1-5 of the drawings which illustrate astand-up plastic bag, generally designated 10 and comprising oneembodiment of a bag produced by the method of the present invention. Inits basic components, the bag 10 includes a pair of front and rear sidewalls 12, 14 and a pair of front and rear bottom gusset walls 16, 18(see FIGS. 2-5). The side walls 12, 14 define an open mouth 20 for thebag 10 between upper edges 12A, 14A of the walls 12, 14. The front andrear bottom gusset walls 16, 18 are disposed between the side walls 12,14 and each have respective upper and lower portions 22, 24 and 26, 28.The upper portions 22, 26 of the gusset walls 16, 18 are integrallyconnected and foldable relative to one another about a center fold line30. The upper portions 22, 26 of the gusset walls 16, 18 are integrallyconnected and foldable relative to the respective lower portions 24, 28thereof about front and rear fold lines 32A, 32B. Also, the lowerportions 24, 28 of the gusset walls 16, 18 at their lower edges 16A, 18Aare integrally connected and folded relative to the lower edges 12B, 14Bof the side walls 12, 14.

Referring specifically to FIG. 2, there is illustrated a cross-sectiontaken through lower end portions 34, 36 of the front and rear side walls12, 14 corresponding to the lower end portions 24, 28 of the front andrear bottom gusset walls 16, 18. The composition of the film of whicheach of the walls 12-18 is formed is depicted most clearly in FIG. 2wherein it is illustrated that the film is multi-layered, being composedof two different heat-sealable thermoplastic materials 38 and 40 and anadhesive or glue material 42 there between bonding the two thermoplasticmaterials together. It is important that the thermoplastic materialsselected be heat-sealable at different ranges of temperatures.Particularly, the material 38 which ultimately will be on the interiorsurfaces of the walls 12-18 must be heat-sealable within a temperaturerange which is lower than the temperature range at which the material 40on the exterior surfaces of the walls 12-18 will be heat sealable.Maintenance of this difference in heat sealing temperature rangesbetween the exterior and interior surfaces of the walls 12-18 isimportant in order to avoid heat sealing together the facing exteriorsurfaces 44, 46 of the front and rear bottom gusset walls 16, 18, shownin FIG. 2, at the same time that the interior surfaces 48, 50 of theirlower end portions 24, 28 which face interior surfaces 52, 54 of thelower end portions 34, 36 of the front and rear side walls 12, 14 areheat sealed thereto as will be described in detail below.

By way of example, the preferred composition of the film is amulti-layer coextrusion of Nylon (polyamide)/glue/PE (polyethylene) inthicknesses of about 0.1-1.0 mils, 0.1-0.5 mils, and 0.5-5.0 mils,respectively. Bag stability has been found to increase with film modulus(stiffness). The heat sealing temperature range of the polyethylenematerial 38 is from about 125° to 190° C. The preferred temperature forheat sealing the material 38 on the interior surfaces of the walls 12-18is approximately 130° to 150° C. The heat sealing temperature range ofthe Nylon material 40 is from about 190° to 280° C. The preferredtemperature range for heat sealing the material 40 on the exteriorsurfaces of the walls 12-18 is approximately 210° to 250° C. Othermaterials, thicknesses and heat sealing temperature ranges are possible.For example, thermoplastics like polycarbonate, polyester,polyvinylidene chloride, poly-4-methyl-1-pentene, polyphenylene sulfideand other higher temperature sealing thermoplastics may be substitutedfor the Nylon and other polyolefins, polyvinylchloride, ethylene vinylacetate, polystyrene, polyisoprene, and other lower temperature sealingthermoplastics may be substituted for the polyethylene.

The preferred composition of the film is particularly well suited for astand-up bag to hold hot liquids--i.e. it may be used for boiling watertemperature liquids in either microwave or in boiling water heating. TheNylon layer has high modulus and high heat distortion features which addto hot liquid stand up stability and boiling water performance.

The preferred composition of the film is also particularly well suitedfor freezer use. The relatively thick polyethylene layer providestoughness and flexibility even at freezer temperatures.

Referring still to FIG. 2, as well as FIG. 1, it will be seen that theupper portions 22, 26 of the front and rear bottom gusset walls 16, 18are interconnected together to define a bottom wall 60 which extendsbetween the front and rear side walls 12, 14 and which, because of theother features of the bag of the present invention, will present arelatively flat support base when the bag is in use. Thus, the lower endportions 24, 28 of the front and rear bottom gusset walls 16, 18 arejoined by heat seals 62, 64 to lower end portions 34, 36 of the frontand rear side walls 12, 14 at contiguous portions of the thermoplasticmaterial 38 on their respective interior surfaces 48-54. Theconfiguration of the bottom wall 60 preferably either is concave-shaped,as shown in the first embodiment of FIG. 1, or has a shape wherein theopposite end portions of the bottom wall are oppositely inclined atabout forty-five degrees as shown in the second (and preferred)embodiment of FIGS. 7-8, discussed in more detail below. Also,preferably, several limited regions 65 between the respective interiorsurfaces 48-54 of the gusset and side wall lower end portions 24, 28,34, 36, as outlined in FIGS. 1, 6B, 7 and 8 are left unsealed tominimize the amount of distortion which ordinarily results from the heatsealing process. Regions 65 also provide a "cool corner" for the user tohold onto when emptying hot contents from the bag.

Simultaneously, the opposite right longitudinal edges 72 and leftlongitudinal edges 74 of the front and rear side walls 12, 14 are joinedwith the aforementioned right longitudinal edges 66, 68 and leftlongitudinal edges of the gusset walls 16, 18 by heat seals 76 formed atcontiguous portions of the thermoplastic material 38 on interiorsurfaces thereof, as shown both in FIGS. 3 and 4. These heat seals 76provide a reliable, leak-proof seal along the opposite longitudinaledges adjacent the non-gussetted portion of the bag 10. As seen in FIG.3, an additional end seal 78 can be provided between the thermoplasticmaterial 40 on the exterior surfaces of the longitudinal edges 72, 74 ofthe side walls 12, 14 if the bags 10 are severed from one another byusing a hot wire or hot knife severing technique. However, thisadditional seal is not essential. A guillotine knife cut at the centerof the bar seal is preferred for the sake of process simplicity.

As shown in FIGS. 4 and 5, the opposite right longitudinal edges 66, 68and left longitudinal edges of the front and rear bottom gusset walls16, 18 of FIG. 1 are joined by the formation of respective heat seals70. Only the right longitudinal edges 66, 68 of the gusset walls 16, 18and the right heat seal 70 are shown in detail in FIG. 5. The heat seals70 are formed at contiguous portions of the thermoplastic material 40 onthe facing exterior surfaces 44, 46 (see FIG. 2) thereof at thelongitudinal edges 66, 68 adjacent the gussetted portion of the bag 10.

As seen in FIG. 1, the bag 10 also may preferably include an openableand closable closure device 80 of any suitable conventional designalthough a zipper-type closure device is preferred. The device 80 isdefined on the front and rear side walls 12, 14 just below and adjacentto the bag mouth 20 defined at the upper edges 12A, 14A, thereof. Thecomponents 80A, 80B of the closure device 80, as seen schematically inFIG. 6, can be integrally formed on the film 82 or laminated thereon.

Turning now to FIGS. 6 and 6A-6C, the steps involved in the method ofthe present invention for making the stand-up reclosable plastic bag 10are shown in block form and the states of a bag at the various stages inits formation are illustrated. The process may be a continuous, asemi-continuous, or a multi-step batch process. The components used inthe method are individually well-known in the art and to illustrate themin detail herein would not make it easier to understand the method ofthe present invention. The components used in the method herein aregenerally the same as components schematically illustrated in theafore-cited U.S. patents to Doyen et al and Kan. The differences residenot in the components per se but in the steps as they are employed tocarry out the method of the present invention.

A web of the multi-layered film 82 is supplied from a roll 84.Alternatively a web of multi-layered film 82 may be supplied directly,as fabricated, from an extrusion and/or laminating line. As describedabove, the film 82 has the two different thermoplastic materials 38, 40(FIG. 2), for instance polyethylene and Nylon, which are heat-sealableupon applying heat at temperatures within different ranges, as describedpreviously.

Prior to reaching the first heat sealing station, the film 82 is foldedto form the front and rear side walls 12, 14 and to form the front andrear bottom gusset walls 16, 18 (FIGS. 1 and 2) which are disposed andfolded inwardly between the side walls so that the Nylon andpolyethylene materials are respectively on the interior and exteriorsurfaces of the side and gusset walls, as was described previously.Also, the components 80A, 80B of the closure device 80 are locked orclosed. The state or condition of a partially completed bag just beforereaching block 88 would resemble that depicted in FIG. 6A.

Block 88 represents the applying of heat, by use of shoe or bar-likemembers, to join simultaneously the lower end portions 24, 28 of thegusset walls and lower end portions 34, 36 of the side walls 12, 14 attheir interior surfaces for forming the bottom gusset heat seals 62, 64,and the front and rear side walls 12, 14 with the front and rear bottomgusset walls 16, 18 along the opposite longitudinal edges thereof atcontiguous portions of the polyethylene material 38 on their interiorsurfaces forming side seam heat seals 76 (FIG. 2). The application ofheat within the lower one of the two aforementioned temperature rangescauses joining of the lower end portions at their interior surfaces, butnot at their exterior surfaces, by forming the above-described bottomgusset heat seals 62, 64 and side seam heat seals 76 in FIG. 2 and asrepresented by the dotted regions in FIG. 6B. That figure shows thecondition of the partially completed bag after leaving block 88.

Formation of the bottom gusset seals 62, 64 and side seam seals 76 in asingle step provides seals which are in correct alignment in thefinished bags. Further, combining these two sealing steps into a singlestep increases the efficiency of the production process and reducesequipment costs.

Block 90 represents forming gusset edge heat seals 70 (FIG. 5) to jointhe front and rear bottom gusset walls together along the oppositelongitudinal edges thereof at contiguous portions of the Nylon material40 on the exterior surfaces thereof, as described above. To form theheat seals 70, heat is now applied to the gusset wall edges at atemperature within the higher temperature range using conventionalsealing bars as depicted by the dotted regions in FIG. 6C.

Block 90 can also represent a combined or separate step of separatingthe film 82 through into completed plastic bags by severing the filmthrough at each of the heat seals at each of the longitudinal edges ofthe walls. If the sealing and severing are combined, then a conventionalhot wire or hot knife is used. However, if they are performedsuccessively, then a tab sealing bar is used to seal the gusset edgesfollowed by an unheated conventional severing knife.

Referring now to FIGS. 7-8, there is shown a second and preferredembodiment of bag 10. The preferred stand-up, reclosable bag shown inFIGS. 7-8 is made by the same procedure shown in FIG. 6 and utilizes thesame materials and structural elements described with reference to FIGS.1-5 and, therefore like reference numerals have been used.

However, unlike the bag illustrated in the first embodiment of FIGS. 1-5wherein a concave-shaped bottom wall 60 is used, the bag of FIGS. 7-8has a bottom wall with end portions oppositely inclined at aboutforty-five degrees. This is best seen in FIG. 8 where center fold line30 is horizontal in the middle portion thereof, but has an approximate45° incline at the ends 30A and 30B, thereof.

The use of approximate 45° angles at ends 30A and 30B of center foldline 30 results in flat bottom with an essentially rectangular base.That design has been found to be the most stable. In particular itoptimizes hot liquid stability with the bag either open or closed. Thisis because the bag design of FIGS. 7-8 has a lower center of gravitywhich is especially important with hot liquids. A hot liquid softens thebag film and the softened bag tends to "sag" more than an unheated bag.The lower center of gravity better accommodates the "sag" and preventsthe bag from tipping over under those conditions.

Having thus described the stand-up plastic bag and method of making sameof the present invention in detail and by reference to a preferredembodiment thereof, it will be apparent that certain modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A method of making a stand-up plastic bag,comprising the steps of:(a) supplying a multi-layered film of first andsecond thermoplastic materials, said first material being heat-sealableat a temperature within a first temperature range and said secondmaterial being heat-sealable at a temperature within a secondtemperature range which is a range of temperatures higher than thetemperatures in said first temperature range; (b) folding said film toform a pair of front and rear side walls and a pair of front and rearbottom gusset walls disposed between said side walls with said first andsecond materials being on respective interior and exterior surfaces ofsaid side and gusset walls; (c) heat sealing at a temperature withinsaid first temperature range to simultaneously form a first set of heatseals which (1) joins lower end portions of said front and rear bottomgusset walls with corresponding lower end portions of said front andrear side walls at contiguous regions of said first material on saidinterior surfaces thereof to form a bottom wall of connected upperportions of said front and rear bottom gusset walls which extend betweensaid front and rear side walls, and (2) joins said front and rear sidewalls with said front and rear bottom gusset walls along oppositelongitudinal edges thereof at contiguous portions of said first materialon interior surfaces of said longitudinal edges of said walls; (d) heatsealing at a temperature within said second temperature range to form asecond set of heat seals which joins said front and rear bottom gussetwalls together along their opposite longitudinal edges at contiguousportions of said second material on said exterior surfaces thereof; and(e) separating said film into completed plastic bags by severing saidfilm through at each of said heat seals at each of said longitudinaledges of said walls.
 2. The method of claim 1 in which said firsttemperature range is from about 125° to 190° C.
 3. The method of claim 2in which said temperature within said first temperature range ispreferably approximately 130° to 150° C.
 4. The method of claim 1 inwhich said second temperature range is from about 190° to 280° C.
 5. Themethod of claim 4 in which said temperature within said secondtemperature range is preferably approximately 210° to 250° C.
 6. Themethod of claim 1 in which said film is a web formed by coextrudinglayers of said first and second thermoplastic materials.
 7. The methodof claim 1 in which said film contains components of a closure devicethereon.
 8. The method of claim 1 in which there is a straightforty-five degree heat seal at the opposite lower end portions of saidfront and rear side walls and said front and rear gusset walls.